Equipment for forming photolithographic reduction images of microcircuit devices is under heavy pressure to improve or reduce the resolution dimension of elements in the imaged device while also imaging larger devices having bigger overall dimensions and containing ever-increasing numbers of finely resolved elements. The optical challenge of producing a microlithographic reduction lens that is free enough of aberration and distortion to meet the desired resolution range of 0.1-0.50 .mu.m is already formidable; and to add the requirement that the microcircuit device become even larger compounds the difficulty of solving all the optical problems.
We have devised a solution that can use the best available photolithographic reduction lenses, without increasing the size of the axial image field of such lenses, to image microcircuit devices larger than will fit within a single image field. This allows well-understood and reliable lens systems, as they have evolved for present day "steppers," to be used in a different way that forms fine resolution images of microcircuit devices larger than such lenses can image in a single exposure. Our invention advances the capability of the best axially centered, photolithographic reduction lenses so that they can image microcircuit devices in extended fields that were not previously possible.